This invention relates to a non-broadcast multi-access (NBMA) network system which employs Next Hop Resolution Protocol (NHRP), more particularly, to a system for the transmission of NHRP packets.
In general, Next Hop Resolution Protocol (NHRP) is used as an address resolution protocol in a non-broadcast multiaccess (NBMA) network and has been discussed in the Internet Engineering Task Force (IETF). The specifications of the NHRP may be, for example, written in draft-ietf-rolc-NHRP-08.txt.
A description of NHRP will be made hereinunder. It will be assumed that an ATM network is used as the NBMA network and that the Internet Protocol (IP) is used as a higher-level protocol although the same discussion applies even when other types of NBMA network and network layer protocol are employed.
In order to perform IP communications over the ATM network, it is necessary to acquire an ATM address from the IP address of a recipient. An NHRP server (NHS) is provided in each individual area (for example, logical IP subnet, or LIS). The NHRP server locally manages data on combinations of IP addresses and ATM addresses of individual ATM stations connected to the ATM network in the NHRP.
In a case where an ATM station discovers an ATM address that corresponds to the IP address of a specific recipient, the ATM station transmits an NHRP address resolution request packet to a predetermined NHS. Upon receiving the NHRP address resolution request packet, the predetermined NHS returns an NHRP address resolution reply packet to the ATM station when it is possible to determine the requested ATM address. When it is impossible for the predetermined NHS to determine the requested ATM address, the predetermined NHS transfers the NHRP address resolution request packet to another NHS which is supposed to have address conversion data on the relevant IP address. This means that the NHRP address resolution request packet is transferred from one NHS to another until it reaches an NHS which can perform the requested address resolution operation.
It is therefore possible to discover the ATM address of the recipient when it is directly connected to the ATM network, even if the recipient belongs to a different LIS. In case where the recipient is not directly connected to the ATM network, it is possible to provide the ATM address of an exit router (gateway) of the ATM network.
Each NHS determines whether it should process a received NHRP packet depending on whether it is the very NHS which is assigned to manage the destination of the relevant packet. The received NHRP packet may be, for example, the aforementioned NHRP address resolution request packet. The destination would be an IP address to be resolved when the received packet is an NHRP address resolution request packet. The destination would be an IP address to be registered when the received packet is an NHRP registration request packet. The destination would be an IP address designated in a destination IP address field of the NHRP packet when the received packet is other than the NHRP address resolution request and NHRP registration request packets. It is stipulated that the NHS must determine to which other NHS the received NHRP packet should be transferred by reference to an IP routing table stored in the NHS if it judges that it is not assigned to process the received NHRP packet.
Conventional rules for NHRP packet transfer under the NHRP have been associated with a problem, namely that has been required to register IP addresses to be managed by each individual NHS. Each NHS performs NHRP packet transfer operation referring to an IP routing table. Another problem is that it is not possible to transfer an NHRP packet to the right NHS which manages a relevant LIS only by referring to the IP routing table if a plurality of NHS's belong to a specific LIS and it is desired to assign only one of these NHS's to manage address information of that LIS.